hello guys,,,im building a 58 bealir w/straight 6 235 and im almost completed,but having a few problems i cant figure out this vacumn deal when i shift into gear , it shifts really hard so i replaced the transmision modulator and still shifts hard, i replaced all vacumn lines. transmission fluid is right, ive tried adjusting the idle. i have one vacumn line that comes off exhaust manifold under carb and goes to a Tee, from the tee one goes to the fuel pump(whats that for ?) and one goes to the transmission modulator. isnt another supposed to go to the windshield wipers? i still cant figure out whats going on with it,,i figured maybe i could get on here and you old guys could help me out thanks a lot <!--POLLS--><!--FILES--><!--SIGNATURE-->
I am going to take a (poor) stab at this. I don't think the vacuum modulator has ever been getting a vacuum. The fuel pump is the source for your vacuum. Buicks and others did this, I didn't know Chevy did. The hose with a vacuum should go to the windshield wiper moter. I do not know if it has enough vacuum to power the modulator. I don't understand the exhaust manifold thing unless you are plumbed into the heat tube that runs from the center of the exhaust manifold and goes directly into the choke control on the pass. side of the carb. No vacuum line should be tied to that. If it is, your pump is never able to creat the vacuum you are needing-it is sucking on an open line. Most guysp lumb the vacuum modulator into the intake manifold. If there is a place to do that, it will be behind the carb, I think you could also hook into one of the vacuum ports on the carb, but I don't know that it will make enough vacuum to work the modulator. Be sure to use a metal line to the carb. if ppossible-don't want the vacuum to collapse the long rubber hose you will be tempted to use. And I'm not THAT old.
vacuum to the transmission modulator must come from the intake manifold, and not go to anything else. And it should have nothing to do with how it shifts into gear from neutral...that's an idle speed issue, or the trans is messed up internally (too much line pressure, missing wavy plate in clutch if it had one, etc)
ok, ill try to just run a sigle line from intake straight to modulator,,,so all the other vacumm should be coming off the fuel pump? thanks
The modulator needs to sense the load on the engine by sensing the vacuum signal directly from the manifold. A dual action fuel pump uses the second diaphragm on top to boost the vacuum from the manifold to run the vacuum wipers. Going up a hill puts a load on the engine and the vacuum drops and the wipers would slow down or even stop. You would have to lift off the gas pedal real quickly to get a single wipe and then back on the gas pedal. The tube should run from the manifold to the top of the fuel pump and onto the wiper motor. Check a shop manual for the correct routing if it matters to you. You will need to know which is the intake tube coming from the intake and the discharge tube going to the wipers. The tube that comes off of the exhaust manifold most likely goes to an automatic choke on the carb. Get a reproduction shop manual to make sure.. I got a dual action pump for my FE engine for my 56 Ford. Most people will say get an electric replacement wiper. I enjoy the old stuff. I can't justify the cost for the few times I might get caught in a storm. I got through several storms just fine in my 36 Ford with the original restored wipers. Besides I'm sure I'll get a few questions about that funky looking fuel pump.
FWIW: What automatic are you talking about here? Powerglide or Turboglide? The Turboglide used the modulator for smooth application of the GRADE RETARDER clutch. The Powerglide has a modulator too, but for what reason, have no idea? Maybe for smooth application of the ranges.
ok that maybe it,,,sounds like i have a closed loop besides the one going to the modulator...i give that a shot,,,so run a single line from intake manifold to the modulator(powerglide) then the one coming off the carb goes to the fuel pump,,off the fuel pump going to windshield wipers......ive heard not getting good vacumm to the modulator would cause harsh shifting....
Need direct vacuum from intake to the trans modulator as the guys mention.... when shifted to "D" on the power glide , the low band applies. A tube from the exhaust manifold would be a hook up for heat to the choke on the carb IF it has an automatic choke setup.. this is usually a steel tube, not rubber hose
ok cool,,,ya it doesnt have a choke on it...just the steel tube line running to the fuel pump. thanks for your help guys
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